Ferroelectric ceramic materials are used in various industrial applications as dielectric media to produce electronic components or devices such as piezoelectric sensors, actuators, transducers, capacitors and pyroelectric sensors. During the manufacturing process of these devices, ferroelectric ceramic materials is are to undergo a sintering process at a high temperature. For example, at a temperature of about 1000° C. or higher. However, sintering at a high temperature significantly limits the application of ferroelectric ceramic material and leads to high manufacturing costs, and even cause device failures.
For example, in the manufacturing process of multilayer capacitors and actuators, dielectric layers made of ferroelectric ceramic materials are co-fired with the metal electrode layers laminated between the dielectric layers. To withstand the high sintering temperature, the electrode layers are required to possess excellent chemical inertness in oxygen ambient. Presently, the electrode layers are often made of precious metals such as Palladium-Silver (Pd—Ag) or Platinum (Pt). The cost of the electrode layers made of these precious materials is high, which can amounts to up to 80% of the total material costs of the multilayer devices. To stay competitive in the industry, manufacturers are continuously seeking every possibility to reduce the cost of the products they make, one approach of which is to use high silver-content alloy with reduced Pd amount to make the electrodes. However, this approach is difficult to implement because the high silver-content alloy and base metal cannot sustain the sintering temperature required for the conventional ferroelectric ceramic materials, when the sintering process is carried out in oxygen ambient.
In another example, piezoelectric devices are fabricated with ferroelectric ceramic thick films formed on a bottom electrode layer and substrate. During the fabrication process, the bottom electrode and substrate are to sustain a sintering temperature of about 1000° C. or higher. However, this sintering temperature will cause serious inter-diffusion and oxidation of the metal electrode layer and substrate, which may result in failure in the integration of a ferroelectric ceramic thick film on a metallized substrate. Therefore, a reduction in sintering temperature is highly desirable to improve the material and processing compatibilities for integrating a piezoelectric ceramic thick film, as well as to reduce lead evaporation during the sintering process.
Several approaches have been proposed to reduce the sintering temperature of ferroelectric ceramic materials. These approaches include liquid phase sintering, chemical doping, and use of nano-sized ceramic powders. While these approaches may reduce the sintering temperature, the properties of the ferroelectric ceramic devices, in particular the piezoelectric properties of the sintered material are seriously compromised. As such, ferroelectric ceramic materials prepared by these approaches may not satisfy the requirements for fabricating the electronic or electromechanical devices.
In view of the above, what is needed is to provide a ferroelectric ceramic material that may be sintered at a lower temperature and in the meantime, possesses the desired properties suitable for fabricating electronic or electromechanical devices. However, an ideal this type of ferroelectric ceramic material is currently unavailable.